High-dose methotrexate (MTX) with leucovorin rescue has been used clinically and very effectively in the treatment of many neoplastic diseases. However, there are still many complications, such as nephrotoxicity, which frequently occur and are dose-related. The major objectives of our project are to elucidate the mechanisms of such nephorotoxicity and to develop a drug combination which will improve the therapeutic effectiveness and decrease the renal toxicity of MTX. Utilizing our experience acquired from renal transport studies over its past 20 years, we will determine the localization of tubular handling of MTX and electronmicroscopic picture of the kidney after administration of MTX. We plan to synthesize a new series of compounds which are analogous to MTX and p-aminohippurate. We will study the tubular secretory rate of these compounds and determine the following: whether they compete for the same transport mechanism as MTX; whether they prolonged the t1/2 of MTX; and whether they reduce the renal toxicity caused by MTX. We also plan to assess the hematotoxicity of these compounds as well as MTX in experimental animals and myelosuppressive effect in man in vitro culture technique. We plan to demonstrate whether these agents can synergize the inhibitory effect of MTX in the presence of leucovorin. Our project is significant in that it will promote an understanding of the nature, the characteristics and the prevention of MTX nephrotoxicity. With the help of the new compounds, a new treatment regimen for MTX may be established which will substantially reduce the cost of high-dose MTX therapy of cancer.